1. Field of the Invention
The invention relates to a production method for an electrode for a battery, an electrode produced by the production method, and a battery including the electrode.
2. Description of the Related Art
In a secondary battery, a portion of chemical energy is converted to electric energy due to a chemical reaction. Thus, electricity is discharged from the secondary battery. In addition, when current flows in a direction opposite to a direction in which current flows at the time of electric discharge, electric energy is converted to chemical energy, and stored in the secondary battery (that is, the secondary battery is charged). Among secondary batteries, a lithium secondary battery is widely employed as power sources of, for example, a notebook-sized personal computer and a cellular phone, because the lithium secondary battery has high energy density.
In the lithium secondary battery, when graphite (C6) is used as a negative electrode active material, a reaction represented by a formula (1) proceeds at a negative electrode at the time of electric discharge.C6Li→C6+Li++e−  (1)Electrons generated in the formula (1) flow through an external circuit, and perform work on an external load, and then, reaches a positive electrode. Lithium ions (Li+) generated in the formula (1) move in an electrolyte held between the negative electrode and the positive electrode, from the negative electrode to the positive electrode due to electro-osmosis.
When lithium cobaltate (Li0.4CoO2) is used as the positive electrode active material, a reaction represented by a formula (2) proceeds at the positive electrode at the time of electric discharge.Li0.4CoO2+0.6Li++0.6e−→LiCoO2  (2)At the time of electric charge, a reverse reaction opposite to the reaction represented by the formula (1) proceeds at the negative electrode, and a reverse reaction opposite to the reaction represented by the formula (2) proceeds at the positive electrode. At the negative electrode, the graphite (C6Li), into which the lithium ions have moved due to graphite intercalation, is recovered. At the positive electrode, lithium cobaltate (Li0.4CoO2) is recovered. Thus, the lithium secondary battery is able to discharge.
It is known that in a conventional solid lithium secondary battery, when a thin film of LiCoO2, which is used as the positive electrode active material, is produced, there is a strong tendency of the c-axis orientation (that is, the (003) plane orientation), and therefore, Li ions are not smoothly transmitted between the positive electrode active material and a solid electrolyte, and as a result, the output current of the all-solid lithium secondary battery is decreased. In order to solve the problem, Japanese Patent Application Publication No. 2003-132887 (JP-A-2003-132887) describes a technology regarding a solid lithium secondary battery, as a technology in which the c-axes of lithium cobaltate crystals are inclined with respect to the normal line of a substrate. In the solid lithium secondary battery, a positive electrode active material layer made of LiCoO2, an electrolyte layer, and a negative electrode active material layer are sequentially formed on a conductive substrate. The c-axes of the crystals of the positive electrode active material LiCoO2 are inclined at an angle of at least 60° with respect to the normal line of the substrate.
In the publication No. 2003-132887, a layer of LiCoO2, which is the positive electrode active material, is formed on the conductive substrate by the gas phase film forming method, as described in the paragraph 6 in the publication. However, when employing the gas phase film forming method, it is difficult to set the thickness of the positive electrode active material layer to a large thickness. Accordingly, when producing a battery in which the positive electrode active material layer has a large thickness, that is, when producing a battery with a high discharge characteristic, the gas phase film forming method is not practical.